quantum density fluctuations presentshortly after the big bang,” says Madau.“The ordinary matter that forms starsand planets has fallen into the gravita-tional wells created by large clumps ofdark matter, giving rise to galaxies inthe centers of dark matter halos.”Even smaller, on stellar scales, as-tronomers have employed HPCs torender a clearer picture of why a classof compact, dense objects called neu-tron stars often move through spaceat very high velocities, in some cases1,000 kilometers or more per second.(Most stars have typical space veloci-ties of a few tens of kilometers persecond.) A clue may be found in howneutron stars are created. These ob-jects, in which protons and electronshave been gravitationally compressedinto neutrons, form from the collaps-ing cores of massive stars just beforethey explode as supernovae. Most as-tronomers have long been convincedthe explosion itself somehow gives theneutron star its high-velocity “kick.”To explore this possibility, Adam Bur-rows, an astrophysicist at PrincetonUniversity, created a three-dimension-al animation of conditions through-out the star during the explosion. Hefound that the star does not explodesymmetrically, but that the explosionrips through the star asymmetrically.The hydrodynamic recoil from suchan explosion is more than sufficient tohurl the neutron star off into space.

“This is a straightforward conse-quence of momentum conservationwhen things aren’t spherical,” saysBurrows. “A lot of exotic mechanismshave been proposed, but this simplestof origins seems quite natural.”The simulation was run on the CrayXT5 Kraken supercomputer, which isthe 21st most-powerful computer in theworld, and is housed at Oak Ridge Na-tional Laboratory.

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Blue Waters project is now online at
the National Center for Supercomputer Applications in Urbana-Champaign,
IL. Titan should become operational
at the Oak Ridge National Laboratory
later this year, and Stampede at The
University of Texas at Austin is expected to be up and running in January
2013. These and other HPCs promise
to reveal new and transformative insights into the world and the universe
from the smallest scales to the largest.
Their simulations will probe levels
of complexity we can only imagine,
taking us where no one has gone—or
could possibly go—before.